Jabbed with a sharp needle, confined in a noisy MRI machine, covered with an anesthesia mask before surgery. Hospital experiences are unpleasant enough for adults. For children, they can be especially stressful and frightening.

More children are facing painful and invasive procedures, as medical advances have made survival possible for more premature infants and children with diagnoses including cancer, cerebral palsy, cystic fibrosis and congenital heart defects. Some three million children are considered "medically...